Hollow fiber membrane filtration modules are commonly used to separate solid components from a liquid containing those components. These filtration modules typically contain several bundles of hollow fibers which serve as the filtering element. The bundles are usually arranged uniformly around a hollow pipe so that liquid is filtered through the fibers and collected in the pipe for removal from the module.
Hollow fiber membrane filtration modules typically contain an outer housing having a longitudinal axis and raw inlet and outlet ends. The hollow pipe is generally located along the longitudinal axis of the outer housing and has a plurality of perforations for guiding filtered liquid from the module. A non-porous member is attached to each end of the outer housing to form a seal between the hollow pipe and the outer housing. The hollow fibers are arranged in an annular space formed between the hollow pipe and the outer housing. The fibers are secured by and penetrate through the nonporous members to form channels for raw liquid to pass through the module. The hollow fibers filter raw liquid by selectively passing liquid through their walls.
During operation of the filtration module, the pressure required to force the feedstock liquid through the hollow fiber membranes must be gradually increased. This occurs due to the accumulation of solids (i.e., fouling components) in the pores of the hollow fiber membrane. This accumulation of solids affects the duration of each processing cycle. Indeed, the duration of each processing cycle is determined by a variety of factors, such as, for example, type of fouling components, filtrate flow, recovery ratio, desired period between cleanings, and the like.
Various backwashing procedures have been developed to remove fouling components from hollow fibers. Backwashing generally involves forcing a liquid through the hollow fiber membranes, which dislodges solids entrapped within the membrane. The efficiency of backwashing procedures directly effects the overall efficiency of the filtration module. Accordingly, there is a continuing need for improved backwashing procedures for hollow fiber membrane filtration modules.